Descartes’s Independence Conception of Substance and His Separability Argument for Substance Dualism

I critically examine the view that Descartes’s independence conception (IC) of substance plays a crucial role in his “separability argument” for substance dualism. I argue that IC is a poisoned chalice. I do so by considering how an IC-based separability argument fares on two different ways of thinking about principal attributes. On the one hand, if we take principal attributes to be universals, then a separability argument that deploys IC establishes a version of dualism that is unacceptably strong. On the other hand, if we take principal attributes to be tropes, then IC introduces challenges which undermine the argument. This is partly because the assumption of tropes makes it possible to distinguish several versions of substance dualism, versions which differ with respect to their degree of generality. I argue that taking principal attributes to be tropes makes it challenging to establish any of these versions by way of an IC-based separability argument. I conclude the paper by suggesting a way forward for the proponent of the separability argument.